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  <section id="cmp0126">
<span id="policy:CMP0126"></span><h1>CMP0126<a class="headerlink" href="#cmp0126" title="Permalink to this heading">¶</a></h1>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.21.</span></p>
</div>
<p>When this policy is set to <code class="docutils literal notranslate"><span class="pre">NEW</span></code>, the <span class="target" id="index-0-command:set"></span><a class="reference internal" href="../command/set.html#cache" title="set(cache)"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">set(CACHE)</span></code></a> command does not
remove any normal variable of the same name from the current scope.
The <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior removes any normal variable of the same name from the
current scope in the following situations:</p>
<ul class="simple">
<li><p>No cache variable of that name existed previously.</p></li>
<li><p>A cache variable of that name existed previously, but it had no type.
This can occur when the variable was set on the command line using a form
like <code class="docutils literal notranslate"><span class="pre">cmake</span> <span class="pre">-DMYVAR=blah</span></code> instead of <code class="docutils literal notranslate"><span class="pre">cmake</span> <span class="pre">-DMYVAR:STRING=blah</span></code>.</p></li>
<li><p>The <code class="docutils literal notranslate"><span class="pre">FORCE</span></code> or <code class="docutils literal notranslate"><span class="pre">INTERNAL</span></code> keywords were used when setting the cache
variable.</p></li>
</ul>
<p>Note that the <code class="docutils literal notranslate"><span class="pre">NEW</span></code> behavior has an important difference to the similar
<code class="docutils literal notranslate"><span class="pre">NEW</span></code> behavior of policy <span class="target" id="index-0-policy:CMP0077"></span><a class="reference internal" href="CMP0077.html#policy:CMP0077" title="CMP0077"><code class="xref cmake cmake-policy docutils literal notranslate"><span class="pre">CMP0077</span></code></a>.  The <span class="target" id="index-1-command:set"></span><a class="reference internal" href="../command/set.html#cache" title="set(cache)"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">set(CACHE)</span></code></a>
command always sets the cache variable if it did not exist previously,
regardless of the <code class="docutils literal notranslate"><span class="pre">CMP0126</span></code> policy setting.  The <span class="target" id="index-0-command:option"></span><a class="reference internal" href="../command/option.html#command:option" title="option"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">option()</span></code></a> command
will <em>not</em> set the cache variable if a non-cache variable of the same name
already exists and <span class="target" id="index-1-policy:CMP0077"></span><a class="reference internal" href="CMP0077.html#policy:CMP0077" title="CMP0077"><code class="xref cmake cmake-policy docutils literal notranslate"><span class="pre">CMP0077</span></code></a> is set to <code class="docutils literal notranslate"><span class="pre">NEW</span></code>.</p>
<p>Policy <code class="docutils literal notranslate"><span class="pre">CMP0126</span></code> was introduced in CMake version 3.21. Use the
<span class="target" id="index-0-command:cmake_policy"></span><a class="reference internal" href="../command/cmake_policy.html#command:cmake_policy" title="cmake_policy"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">cmake_policy()</span></code></a> command to set it to <code class="docutils literal notranslate"><span class="pre">OLD</span></code> or <code class="docutils literal notranslate"><span class="pre">NEW</span></code> explicitly
within a project.  Use the <span class="target" id="index-0-variable:CMAKE_POLICY_DEFAULT_CMP&lt;NNNN&gt;"></span><a class="reference internal" href="../variable/CMAKE_POLICY_DEFAULT_CMPNNNN.html#variable:CMAKE_POLICY_DEFAULT_CMP&lt;NNNN&gt;" title="CMAKE_POLICY_DEFAULT_CMP&lt;NNNN&gt;"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_POLICY_DEFAULT_CMP0126</span></code></a> variable to set the policy for
a third-party project in a subdirectory without modifying it.
Unlike many policies, CMake version 3.27.4 does <em>not</em> warn when the policy
is not set and simply uses <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior.  See documentation of the
<span class="target" id="index-0-variable:CMAKE_POLICY_WARNING_CMP&lt;NNNN&gt;"></span><a class="reference internal" href="../variable/CMAKE_POLICY_WARNING_CMPNNNN.html#variable:CMAKE_POLICY_WARNING_CMP&lt;NNNN&gt;" title="CMAKE_POLICY_WARNING_CMP&lt;NNNN&gt;"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_POLICY_WARNING_CMP0126</span></code></a>
variable to control the warning.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior of a policy is
<span class="target" id="index-0-manual:cmake-policies(7)"></span><a class="reference internal" href="../manual/cmake-policies.7.html#manual:cmake-policies(7)" title="cmake-policies(7)"><code class="xref cmake cmake-manual docutils literal notranslate"><span class="pre">deprecated</span> <span class="pre">by</span> <span class="pre">definition</span></code></a>
and may be removed in a future version of CMake.</p>
</div>
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